1. Field of the Invention
The present invention relates to a method for manufacturing a Silicon-On-Insulator (SOI) substrate partially having a buried oxide film in a silicon substrate by a Separation by IMplanted Oxygen (SIMOX) method.
2. Description of the Related Art
It is conventionally expected to use an SOI substrate having a buried oxide film in a silicon substrate for high-speed low-power-consumption device substrates. Among these device substrates, an SOI substrate having a buried oxide film in a silicon substrate not entirely but partially (hereafter referred to as “partial SOI substrate”) is regarded to be important because it is possible to form only a logic portion in an SOI area of a buried oxide film in a system LSI including analog logic memories and to manufacture a memory portion at a bulk Si portion without the buried oxide film.
As this type of method for manufacturing the partial SOI substrate (method for manufacturing SIMOX substrate), the following method (for example, refer to Patent Document 1) is proposed. More particularly, as shown in FIG. 10, a surface oxide film 4 is first formed on the surface of a substrate 2 (substrate 2 is cut in a plane perpendicular to the axis of a single-crystal silicon rod) (FIG. 10 (a))) to form a patterned resist layer 6 on the surface of the surface oxide film 4 through photolithography (FIGS. 10(b) and 10(c)). Then, the surface oxide film 4 is patterned through anisotropic etching (FIGS. 10(d) and 10(e)) to remove the resist layer 6 (FIG. 10F) and then, the substrate 2 is cleaned. Then, oxygen ions 7 are implanted into the surface of the substrate 2 (FIG. 10(g)) and the substrate 2 is immersed in a mixed solution (etching solution) of hydrofluoric-acid ammonium aqueous solution and hydrofluoric acid to remove the surface oxide film 4 (FIG. 10(h)). Moreover, the substrate 2 is held at 1,300° C. or higher for predetermined time in the atmosphere of mixed gas of argon and oxygen or nitrogen and oxygen and is annealed to form a buried oxide film 3 (FIG. 10(i)), then the substrate 2 is immersed in a mixed solution (etching solution) of hydrofluoric-acid ammonium aqueous solution and hydrofluoric acid to remove the surface oxide film 4 (FIG. 10(j)).
Moreover, as shown in FIG. 11, the surface oxide film 4 is formed on the surface of the substrate 2 (substrate 2 is cut in a plane perpendicular to the axis of single-crystal silicon rod) (FIG. 11(a)) and a patterned resist layer 6 is formed on the surface of the surface oxide film 4 through photolithography (FIGS. 11B(b) and 11C(c)). Then, the surface oxide film 4 is patterned through anisotropic etching (FIGS. 11(d) and 11(e)) to remove the resist layer 6 (FIG. 11(f)) and then, the substrate 2 is cleaned. Then, oxygen ions 7 are implanted into the surface of the substrate 2 (FIG. 11(g)), the substrate 2 is held for predetermined time at 1300° C. or higher in the atmosphere of mixed gas of argon and oxygen or mixed gas of nitrogen and oxygen and is annealed to form the buried oxide film 3 (FIG. 11(h)). Furthermore, the substrate 2 is immersed in mixed solution (etching solution) of hydrofluoric-acid ammonium aqueous solution and hydrofluoric acid to remove the surface oxide film 4 (FIG. 11(i)).
However, as shown in FIG. 11(g), when implanting oxygen ions 7 into the substrate 2, the upside of the surface oxide film 4 left on the surface of the substrate 2 as a mask is expanded and deformed due to implantation of oxygen ions 7 and thus the buried depth at the end of the buried oxide film 3 is decreased. Then, an edge area is exposed on the surface of the substrate 2 because the end of the buried oxide film 3 becomes thicker at the time of subsequent annealing. When removing the surface oxide film 4, the edge area is etched, which occasionally causes a concave groove 8 to be formed on the surface of the substrate 2 along the edge area or cavity to be formed on the buried oxide film 3. To dissolve this point, it is proposed to vertically apply anisotropic etching to the surface of the substrate by using the surface oxide film as a mask and vertically implant oxygen ions into the surface of the substrate (for example, refer to Patent Document 2). In this method for manufacturing An SOI substrate, since oxygen ions are implanted in the direction vertical to the surface of a substrate, the edge area of a buried oxide film is not exposed on surface and even if immersing the substrate in an etching solution in order to remove a surface oxide film, the edge area of the buried oxide film is not removed. Therefore, it is possible to prevent an unnecessary concave groove from being formed on the surface of the substrate or unnecessary cavity from being formed on the buried oxide film.
[Patent Document 1] Japanese Patent Laid-Open No. H5-82525 (claim 2)
[Patent Document 2] Japanese Patent Laid-Open No. 2001-308025 (claim 1)